Coal-tar is usually obtained as a by-product of the distillation of coal in coke ovens, e.g. in the manufacture of metallurgical coke. It comprises a mixture of a number of hydrocarbon compounds which can be separated by distillation of the tar. Coal-tar pitch, which is the residue in the still following such a distillation is a viscous material which softens and flows when heated. Pitches are conventionally classified according to their softening points and their solubility in various solvents e.g. quinoline, benzene and dimethylformamide. The latter characteristic is usually indicated by the proportion of the pitch which is insoluble in the solvent e.g. the proportion of the pitch which is quinoline-insoluble (Q.I.) is a widely-used pitch characteristic, and is usually in North America of the order of 12 to 18%. Pitches are also obtained from petroleum but these are different in structures and characteristics especially in degree of aromaticity.
Much of the Q.I. formation takes place at the high temperature to which the tar is subjected during coke formation, and stays in the pitch residue following distillation. The presence of the Q.I. in the tar or pitch can be tolerated for a limited number of applications, however, in most of the uses, the presence of significant amounts of Q.I. is viewed as an undesirable characteristic of the material. The particulate nature of the Q.I. renders difficult virtually any process which requires the passage of the pitch through small orifices; e.g. penetration of pitch is rendered difficult. Additionally, should the Q.I have a high content of ash-forming impurities, the combustion rate of the carbon body produced by coking (or otherwise carbonizing) the pitch will be significantly increased.
Accordingly, it is an object of this invention to provide a process for decreasing and modifying the quinoline-insoluble content in coal-tar material.
It is also an object of this invention to provide a process for obtaining pitch material with a diminished content of quinoline-insoluble material.